For the recent years, the vigorous development of the electro-optic industry, particularly the digital camera and the cellular phone camera, has placed a larger and larger demand for the optical devices. Of the optical elements, the optical lens can be the most essential and important one. In terms of the product characteristics, the optical lens may be categorized into a refractive device (e.g. a lens and a prism), a reflective device, a diffractive device, a hybrid device, among others, which are each related to a specific material and manufacturing process. Among the optical lens, the aspherical optical devices have found more and more applications and are more and more required. This is because the aspherical lens can have a good imaging quality as compared to the spherical lens. Further, when the aspherical optical device is applied to an optical system, the number of the optical device required and the overall cost for the system may be reduced.
For the manufacturing reason, the aspherical lens is prone to a decenter or tilt issue with respect to the optical axes of its two side surfaces, leading to a deviation of the optical characteristics thereof. To obviate the deficient lens products, whether the decenter and tilt issues existing on the two axes of the aspherical lens are required to be measured or inspected, so that the lens itself can be corrected in optical design or manufacturing. In this regard, how to precisely and rapidly measure the aspherical lens is apparently an important issue to the manufacturing and design of the aspherical lens.
For the spherical lens, the optical axis is a line connecting the both curvature centers of the two side surfaces thereof, which is shown in FIG. 7A. For the lens with only a single spherical surface, all lines extending from the curvature center to the spherical surface can be taken as the optical axis, which is shown in FIG. 7B. For the spherical lens, the optical axis is a common line among the optical axes of the two side surfaces and thus the line connected between the two spherical curvature centers. In the spherical lens, the decenter and tilt issues do not exist between the two optical axes but only exists between the optical axes and the geometrical centerlines, which is shown in FIG. 7C. This is conventionally measured by a collimator. In the aspherical lens, a line formed by connecting the curvature centers of all the curvatures of the spherical surfaces is the optical axis and only this optical axis exists therein, which is shown in FIG. 7D. Thus, the aspherical lens is provided with an optical axis at each of the two side surfaces thereof. The two optical axes possibly do not coincide with each other due to the manufacturing error problem. Accordingly, the decenter and tilt issues exist between the two optical axes, which are shown in FIG. 7E. This is generally measured by a reflective collimator. However, the aspherical lens is mostly formed by glass molding or plastic injection and thus burrs and mouse bites might be found at the rim portion thereof, which can cause a disturbance for the rotation of the lens, required when being measured by a collimator, or an error with respect to the measurement.
In view of the above, there is a need to provide a method and device for measuring the decenter and tilt amounts between the two side surfaces of the lens by using an interferometer. After a long intensive series of experiments and research, the inventor finally sets forth such method and device. As compared to the prior art, the method and device of the present invention may not only be used for the spherical lens but also for the aspherical lens, and the optical lens may be precisely and rapidly measured.